The present invention relates to a process for producing petroleum sulfonates and a petroleum sulfonate blend which is useful in enhanced petroleum recovery systems.
Petroleum sulfonates are typical anionic surfactants which contain one or more sulfonate groups per molecule of sulfonated hydrocarbon. These petroleum sulfonates are useful in a variety of applications, including use as surfactants in enhanced petroleum recovery systems. Increasingly important in enhanced petroleum recovery systems is the use of petroleum sulfonates in forming micellar solutions usually comprising a brine, a hydrocarbon, petroleum sulfonate and cosurfactant.
It is known in the art to produce petroleum sulfonates by contacting a crude oil with a sulfonating agent and a neutralizing agent. Crude oils sulfonated in this manner, however, suffer from the disadvantage of containing a wide variety of aromatics and other components which are either under-sulfonated, producing a deficiency of sulfonate product, or over-sulfonated, producing an abundance of highly water soluble polysulfonates. Thus, sulfonated crude oils yield a product sulfonate which exhibits inferior properties for forming micellar solutions useful in an enhanced oil recovery system.
Sulfonation of certain petroleum stocks is known and appreciated by the prior art. But most petroleum stocks produce an undesirable fraction of low equivalent weight sulfonates that are highly water soluble. These low equivalent weight sulfonates are typically lost during enhanced oil recovery operations due to their solubility in reservoir connate waters and in the waters used during flooding operations. To alleviate the disadvantages of low equivalent weight sulfonates, U.S. Pat. No. 4,240,978 discloses a process for producing oil-soluble sulfonates from a vacuum gas oil. Water-soluble sulfonic acids are removed from the effluent of the sulfonation zone to control the percentage of low equivalent weight sulfonates. In this process a mixture of aromatic and paraffinic hydrocarbons having a molecular weight between 250 and 450 is sulfonated with sulfur trioxide. Water-soluble sulfonic acids formed during sulfonation are removed from the effluent of the sulfonation zone by decantation.
Another process for sulfonating petroleum oils, disclosed in U.S. Pat. No. 4,226,805, is designed to remove the very high equivalent weight sulfonates that tend to form a sludge insoluble in either oil or water. In this procedure sulfonates are produced by reacting sulfur trioxide with an aromatic petroleum oil admixed with a liquid sulfonic acid diluent. The resulting product mixture of sulfonated petroleum oil and sludge is allowed to stand so that the sludge settles out from the sulfonated petroleum oil.
U.S. Pat. No. 4,144,266 relates to a process for producing petroleum sulfonates by contacting whole crude oil or topped crude oil, or mixtures thereof, with sulfur trioxide. Unreacted hydrocarbon that tends to form sludge is removed from the reaction product by addition of water, and base is added to neutralize the sulfonic acids formed. Water washing the reaction product also removes the water soluble low equivalent weight sulfonates.
To provide an alternative method of controlling the equivalent weight distribution of the sulfonate product, U.S. Pat. Nos. 3,373,808 and 3,302,713 disclose a process for producing a petroleum sulfonate derived from a 500.degree. F. to 1,500.degree. F. boiling range fraction. Both the low boiling and the high boiling range fractions which are excluded in this process can yield sulfonates of undesirably low equivalent weight. The sulfonates are prepared by direct sulfonation of a petroleum distillate fraction boiling within the above range employing conventional techniques for the sulfonation and neutralization reactions.
U.S. Pat. No. 2,857,426 discloses a method of producing polyvalent metal petroleum oil sulfonates which comprises reacting a refined lubricating oil with a sulfonating agent in the presence of a solvent selected from sulfur dioxide or ethylene chloride. Sulfonic acids thus produced are then reacted with a polyvalent base, such as basic calcium, strontium or barium compounds.